CHAPTER X 



SUBDIVISION 2. ANGIOSPERMAE. PLANTS WITH ENCLOSED 



SEEDS 



122. Origin of the Angiospermae. — These plants, Hke the 

 Gymnospermae, produce seeds, but they differ so essentially from 

 the latter group in the character and structure of the sporophyte 

 and gametophyte as to justify their separation into a distinct 

 division. They are retained here as a group coordinate with 

 the gymnosperms out of deference to common usage. It has 

 been noticed that the seed habit arose quite independently of 

 the Spermatophyta (see page 351) and it appears probable that 

 the Angiospermae represent an independent line of development. 

 Though the most recently evolved plants, their origin is uncertain 

 and the meager evidence points to their derivation from a stock 

 related to the more primative Filicales rather than to the Gym- 

 nospermae. The variations of this modern group of plants have 

 been many and so successful that they have crowded out many 

 of the lower forms and become the dominant plants upon the 

 earth. They exceed all other groups combined in variety and 

 number of forms, approximately, 125,000 species — certainly a 

 striking contrast to the other vascular plants which comprise 

 about 450 gymnosperms and 4000 pteridophytes. The angio- 

 sperms are adapted by their variations to practically all con- 

 ditions that will sustain life, ranging from aquatics to xerophytes, 

 from terrestrials to epiphytes and from photosynthetic to sapro- 

 phytes and parasitic plants. The important features of the 

 plant body have been considered in the opening chapters of the 

 book. 



123. The Sporophylls of Angiosperms. — The flower is often 

 considered as one of the most characteristic features of the 

 angiosperms, but this structure contains as its essential organs 

 one or more sporophylls and the term flower could be applied 

 quite as well to the association of these organs in the Pterido- 

 phyta and gymnosperms. 



378 



